The problem is when I setting up a new DNS domain in ISPconfig interface, that it generated without problem, but the secondary DNS system isn't notified, and also the new domain isn't created.
In the 2nd. system I tried to find the problem, but I can't find anything in the logs. It looks no package sent from main server to 2nd server.

I already enabled allow-update, allow-axfr, notify-enabled and notify-source options in /etc/mydns.conf.
For debugging I changed the log facility to logging to a file (/var/log/mydsn.log). In the log file I find these lines:

Do you also use MyDNS on the slave? Is the slave an ISPConfig mirror, or is there no ISPConfig on that system?

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The 2nd. DNS system is powerdns, and this is not a mirror. Just only a simple CentOS system in the world. It's already configured to accept any communcation over TCP and UDP port 53 from my ISPconfig system (MyDNS).

Mydns can not notify another system for dns changes, for that reason we switched to bind as default dns system in ispconfig. You should consider to replace mydns with bind or as alternative you use the ispconfig dns server mirroring features which would require to install ispconfig on the seconfdary dns too as slave server and let ispconfig configure powerdns.